Locked plate fixation Locked plate fixation ––Principle and applicationsPrinciple and applications

Dr. Edmund WongDr. Edmund Wong16th CUHK16th CUHK--AADOAADO

Comprehensive Comprehensive BioskillBioskill Course on Fracture FixationCourse on Fracture FixationApril 14April 14--16, 200716, 2007

StabilityStabilityStability of fixation is crucial for both Stability of fixation is crucial for both anatomical and biological fixationanatomical and biological fixation

Stability affords early motion to maintain Stability affords early motion to maintain articular surfaces and soft tissuesarticular surfaces and soft tissues

Absolute StabilityAbsolute StabilityStrain at fracture site Strain at fracture site must be less than 2% must be less than 2% for lamellar bone, 10% for lamellar bone, 10% for woven bonefor woven bone

Example compression Example compression platingplating

Lead to primary bone Lead to primary bone healinghealing

Relative StabilityRelative StabilityBased on controlled motionBased on controlled motion

More physiological; leads to More physiological; leads to callus formationcallus formation

Example buttress plating, Example buttress plating, IM nailingIM nailing

Anatomic vs. Biologic FixationAnatomic vs. Biologic Fixation

Anatomic fixationAnatomic fixation--plate maintains the reduction plate maintains the reduction with no motionwith no motion

primary healing (primary healing (endostealendostealhealing)healing)

Cutting cones, creeping Cutting cones, creeping substitution substitution NO CALLUSNO CALLUS

Biologic fixationBiologic fixation--plate bridges the fracture plate bridges the fracture site and allows controlled site and allows controlled motionmotion

secondary healingsecondary healingHematomaHematoma, , inflammation, fibrous inflammation, fibrous tissue, tissue, remodellingremodelling and and differentiation of differentiation of mesenchymalmesenchymal stem cells stem cells to form new boneto form new boneCALLUSCALLUS

Achieving Stability: Overcoming the Achieving Stability: Overcoming the Forces at the Plate Bone InterfaceForces at the Plate Bone Interface

Axial stress (tension and compression)Axial stress (tension and compression)Shear stress at plate bone interfaceShear stress at plate bone interface

1. Axial Load

2. Bending Load

3. Torsion

Stability by plate bone frictionConventional Plate BiomechanicsConventional Plate Biomechanics

Stability by plate bone friction

Periosteal NecrosisPeriosteal Necrosis

Plate/bone interface Plate/bone interface creates creates ““compartmentcompartment””under the plateunder the platePeriostealPeriosteal necrosisnecrosisLCLC--DCP plates only DCP plates only reduce contact by 50%reduce contact by 50%

Remember that Remember that plate/bone interface plate/bone interface crucial for stabilitycrucial for stability

Conventional PlateConventional Plate

2.Movement of plate during axial loading

4.Causes screw to rotate About axis in distal cortex

3. Leading to high stress and bone resorption

Axial Load

1.Screw bending

Conventional PlateConventional Plate

Bending Load

Force applied: screw orients to force. Asthis occurs strength of fixation equals thread pullout strength of single screw at the distal or proximal end of the plate.

Force Axial

Conventional PlateConventional PlateNote: screw plate angle change Limits failure load to that to the strength of thread purchase

Limitations of Conventional PlatesLimitations of Conventional Plates

Failure in osteopenic boneFailure in osteopenic boneGeriatricsGeriatrics

PeriostealPeriosteal avascularityavascularityTissue necrosis under plateTissue necrosis under plate

Percutaneous platingPercutaneous platingPlate elevated off of the bone. No friction between Plate elevated off of the bone. No friction between plate and boneplate and bone

Locking plate - Internal Fixator

Locking head screw

Threaded plate hole

Internal Fixator

Internal Fixator

Internal Fixator

Internal Fixator

Porotic bone

Theoretical AdvantagesTheoretical AdvantagesNo focal necrosis of bone and soft tissue deep No focal necrosis of bone and soft tissue deep to plateto plate…… improved local resistance to infectionimproved local resistance to infection

Avoids early temporary bone losses under plate Avoids early temporary bone losses under plate induced by vascular damageinduced by vascular damage

Strength of fixation equals the sum of all the Strength of fixation equals the sum of all the bolts (screws) ability to resist shear at the boltbolts (screws) ability to resist shear at the bolt--bone interface. Not that of a single screwbone interface. Not that of a single screw’’s s thread purchasethread purchase

Locking PlateLocking Plate

Plate does not haveto contact bone

Axial Load

As Single Beam ConstructScrews Must Shear Through Bone Simultaneously

Locking PlateLocking Plate

Locking PlateLocking Plate

Fixation fails when bolts overcome bone’s resistanceto shear forces. All bolts must fail as a single construct.

Bolt plate interface allows no motion

Screws with angular stability in different directions

Locking plate = internal, external Fixator

Long

Tub

e

Long

Pla

te

Spac

eSp

ace

Spac

eSp

ace

Biomechanical principlessimilar to those of external fixators

Stress distribution

Biomechanical principlessimilar to those of external fixators

Stress concentration

Advantages of int. Fixators

1. Angular Stability of Screws 2. No accurate Plate Contouring

required3.Less Damage to Periosteum4.Less Screw Loosening

1. Angular Stability of Screws

LIFLC-DCP

2. No accurate Plate Contouring required

LIFLC-DCP

3. Less Damage to Periosteum

LIF

LC-DCP

4. Less Screw Loosening

LIFLC-DCP

ApplicationApplication

LCP LCP Locking Compression PlateLocking Compression Plate

Compression Plate and Compression Plate and FixatorFixator

LCP Locking Compression Plate

= DCP + Limited Contact + Locking Holes + = DCP + Limited Contact + Locking Holes + TitaniumTitanium

Some designed for specific sites.Some designed for specific sites.

LCPLCPLocking Compression PlateLocking Compression Plate

LCPLCPLocking Compression PlateLocking Compression Plate

Both a Both a ““plateplate”” and an and an ““internal internal fixatorfixator””Incorporating features of LCIncorporating features of LC--DCP (Limited DCP (Limited Contact DCP)Contact DCP)Used in MIPO, semiUsed in MIPO, semi--open or open fixationsopen or open fixationsUses nonUses non--locking and/or locking head screws locking and/or locking head screws (LHS)(LHS)No external No external ““targettingtargetting”” devicedevice

Locking Screws

Self Taping & Self Drilling

Self Taping

Metaphysealplate

Pre-op planning

• XR

CT

ReductionReduction

TractionTractionExternal fixationExternal fixation

PrePre--contour of platecontour of plate

Insertion of plateInsertion of plate

Place another plate on the surface of skin can guide your percutaneous skin incision for the locking screws.

PrePre--contouredcontouredLocking plate

LISSLess Invasive Stabilisation System

LISSLISSLess Invasive Less Invasive StabilisationStabilisation SystemSystem

A special kind of A special kind of LCPLCPOutOut--rigger for rigger for insertion and insertion and targettingtargettingSo far, only distal So far, only distal femur and proximal femur and proximal tibiatibia

LISSLISS

Aiming device with guide sleeve for self-drilling self-tapping screws (only in LISS)Cooling required!

LISS LISS -- Reservations Reservations ““Less InvasiveLess Invasive”” is surgeon / experience is surgeon / experience dependentdependentDifficult to train / superviseDifficult to train / superviseDoubtful anatomical conformity Doubtful anatomical conformity ––

E.g. E.g. ““anteante--curvaturecurvature”” and size of the femoral and size of the femoral condylecondyle

Not forgivingNot forgivingNot adjustable / revisable once implantedNot adjustable / revisable once implanted

Precaution:Precaution:

Important!

If the first screw to be inserted is a Locking Head Screw, it is important to ensure that the plate shows good temporary fixation. Otherwise, the plate rotates simultaneously when locking the screw, and might cause soft-tissue injuries

Locking Head ScrewsLocking Head Screws

Must be placed in exact Must be placed in exact axial alignment with the axial alignment with the hole on the platehole on the plate

Difficult to angle screws in Difficult to angle screws in plate to obtain osseous plate to obtain osseous purchasepurchase

Drill blocks for selfDrill blocks for self--tapping screws (requiring tapping screws (requiring prepre--drill)drill)

Should the plate lie too ventral or too dorsal, the screws will not be centred in the medullary canal. This position may compromise the screw purchase.

••Limited ability to compress fractureLimited ability to compress fracture••Can not use plate as a reduction aidCan not use plate as a reduction aid•Positioning and Compression Device (PCD)

Skin impingement

Removal of locking screw from the Removal of locking screw from the plate sometimes is difficult: plate sometimes is difficult:

need to prepare broken screw need to prepare broken screw removal setremoval set

The End The End

Thank YouThank You